The present invention generally relates to trainable transmitters, and more particularly relates to vehicle-installed trainable transmitters capable of learning the carrier frequency, modulation scheme, and data code of a received radio frequency (RF) signal.
Trainable transmitters are known that are capable of learning the RF carrier frequency and code of a received RF signal for purposes of subsequently generating and transmitting a modulated RF signal having the learned characteristics on demand. Examples of such RF trainable transmitters are disclosed in U.S. Pat. Nos. 5,583,485; 5,614,885; and 5,379,453 and Italian Patent No. 1,261,150. Such trainable transmitters were designed for implementation in a vehicle accessory such that they can be used to learn the characteristics of a signal transmitted from an original transmitter associated with a garage door opening mechanism. When used in this manner, the trainable transmitter can effectively replace the original transmitter while providing a clean, neat appearance in the interior of the vehicle. Further, these trainable transmitters can be trained to learn more than one activation signal thereby eliminating the need to have more than one transmitting device within a vehicle.
Because some original garage door transmitters sold in the United States utilize different modulation schemes that affect the manner in which the received data code is best encoded and stored in the memory of the trainable transmitters, trainable transmitters were developed that distinguish between different modulation schemes present in a received signal in order to encode such signals in different manners. Commonly-assigned U.S. Pat. Nos. 5,479,155; 5,614,891; 5,661,804; and 5,686,903 disclose trainable transmitters having this added capability.
In the United States, the Federal Communications Commission (FCC) enforces regulations pertaining to the permissible power output of RF signals within certain frequency bands. In the United States, the FCC has designated the frequency band of 200 to 400 MHz for use by RF transmitters of a class including garage door opening transmitters. Because the FCC permits different power levels within this band based on the carrier frequency and duty cycle of the signal and because garage door opening transmitters may have carrier frequencies falling anywhere within this band, trainable transmitters of the type manufactured by the assignee preferably include variable attenuators or amplifiers for varying the amplitude of a transmitted signal in order to transmit the maximum power permitted by the FCC throughout the 200 to 400 MHz band. Trainable transmitters having this capability are described in commonly-assigned U.S. Pat. Nos. 5,442,340; 5,479,155; 5,614,891; and 5,686,903.
To enhance security of garage door opening mechanisms, manufacturers have implemented cryptographic algorithms in their original transmitters and receivers that transmit and respond to randomly varying codes. To enable a vehicle-installed trainable transmitter to effectively operate in such systems, a trainable transmitter was developed that has the capability of recognizing when a received signal has been originated from a transmitter that generates a code that varies with each transmission in accordance with a cryptographic algorithm. When such a variable code is recognized, the trainable transmitter determines which cryptographic algorithm is used to vary the code from one actuation to the next in order to generate and transmit the next code to which the receiver will respond. A trainable transmitter having this capability is disclosed in commonly-assigned U.S. Pat. No. 5,661,804.
Trainable transmitters of the type described above have found other applications and uses within a vehicle. For example, the receiving circuitry in such trainable transmitters may be used to receive and respond to an RF signal transmitted from a remote keyless entry (RKE) key fob to lock and unlock the vehicle's doors and to arm and disarm the vehicle's security system. Such trainable transmitters are disclosed in commonly-assigned U.S. Pat. Nos. 5,614,885; 5,619,190; 5,627,529; and 5,646,701. Additionally, as disclosed in U.S. Pat. No. 5,661,651, the receiving circuitry in a trainable transmitter may also be used to receive vehicle parameter data, such as tire pressure, from transmitters connected to parameter sensors that are mounted within the vehicle. Such an arrangement allows for various vehicle parameters to be monitored and displayed without requiring any additional wiring.
The trainable transmitters described above were developed primarily for use in North America. One problem encountered in developing a trainable transmitter for use in Europe arises from the use in Europe of RF carrier frequencies over a much greater bandwidth than is used in North America. For example, garage door manufacturers sell systems in Europe that transmit at frequencies between a first band of 27 and 40 MHz and between a higher second band of 418 and 433 MHz. The use of carrier frequencies that vary from one another so considerably, poses many practical problems when designing a trainable transmitter that must be capable of learning and subsequently transmitting signals at those carrier frequencies. One such problem relates to the fact that it is difficult to design a single antenna that is efficient at transmitting signals having carrier frequencies falling within both the first and second bands. To solve this problem, PCT Application No. WO 94/02920 discloses a trainable transmitter including two different transmitting antennas for transmitting signals in the two respective frequency bands, as well as a third antenna for receiving signals from within both frequency bands. Another problem relating to the transmission of signals in the two frequency bands arises from the fact that voltage controlled oscillators (VCO) used to generate a carrier signal at such frequencies, become extremely complex and expensive if required to generate carrier signals at frequencies over such a broad range. To avoid this problem, the trainable transmitter disclosed in PCT Application No. WO 94/02920, uses two separate VCOs that may be used to generate the carrier signals within the lower and upper frequency bands. However, the use of two oscillators nonetheless adds to the expense of the device.
In many countries in Europe, garage door opening systems are sold that transmit, receive, and respond to frequency modulated (FM) RF signals. Because essentially all garage door opening systems sold in North America transmit, receive, and respond to amplitude modulated (AM) RF signals and because the trainable transmitters described above (with the exception of those described in PCT Application No. WO 94/02920 and Italian Patent No. 1,226,150) were developed primarily for use in North America, those trainable transmitters do not have the capacity to learn and retransmit an FM signal. The trainable transmitters disclosed in PCT Application No. WO 94/02920 and Italian Patent No. 1,261,150, do not have the capability of receiving, learning, and retransmitting an FM signal. Thus, the prior trainable transmitters are not capable of learning all the various signals used in European garage door opening systems.
An additional problem in developing a trainable transmitter for use in Europe, is to provide the capability in the trainable transmitter to transmit the learned signals at the maximum power levels permitted under all the different regulations of the various countries within Europe. Insofar as the above-described trainable transmitters only vary the amplitude of the transmitted signals based upon the regulations passed by the United States government (if the amplitude is varied at all), and the regulations imposed in many countries in Europe are different from those in the United States, such prior trainable transmitters do not account for these different regulations and therefore do not transmit signals at the maximum power levels allowed by each European country.